It is often necessary to intravenously supply patients with pharmaceutically active liquids at a controlled rate over a long period of time. It is desirable that this be accomplished while the patient is in an ambulatory state. A few devices have been developed in the past for accomplishing this purpose.
The prior art devices typically include an inflatable elastomeric bladder forming a liquid container and have a flow control valve or device and tubing for supply of the liquid to the patient. The walls of the bladder are forced to expand when filled with the liquid, and provide the pressure for expelling the liquid. These prior art devices are typically filled by hand by means of a syringe which often require an inordinate amount of force.
Another drawback to the prior art devices is that the conventional inflatable elastomeric bladder provides pressures and flow rates that can vary widely with the volume of liquid therein. Therefore, they do not have a reasonably stable pressure and flow rate over the infusion period. In addition, such conventional bladders frequently have difficulty dispensing substantially all of the liquid by the end of the infusion period. It is undesirable to have liquid remaining in the bladder.
Various materials are used for constructing conventional inflatable elastomeric bladders. For example, natural rubber is frequently used. Some construction requires several layers of material. The use of silicone in tube form to function as a pressurized liquid reservoir for infusion purposes is described in, for example, U.S. Pat. No. 4,909,790 which discloses an infusion device that uses tubular bladders mounted on mandrel supports with downstream restrictors to deliver uniform flow rates. Another example may be found in U.S. Pat. No. 7,704,230 which describes a pressurized fluid reservoir made from a silicone tube for an infusion system. Such references point to numerous possible combinations of silicones, structural dimensions, filling pressures, operating pressures, and fill volumes. However, the performance provided by the silicone tube disclosed in U.S. Pat. No. 7,704,230 has been found to be unacceptable for use at least because of the variability in flow rate and the pressure during the infusion period and the difficulty dispensing substantially all of the liquid by the end of the infusion period.